This one has a reasonably settled answer, so here it is. The useful checklist is about verifiability rather than presentation. Independent test results commissioned by buyers rather than by the seller, consistency across multiple batches over time rather than one flattering report, a physical address and a company registration that resolve, batch and lot numbers on the actual labelling, and a shipping practice that matches what the material needs. Everything a good-looking website provides is cheap to fake; none of the items above are.

HPLC_Greg said:

The useful checklist is about verifiability rather than presentation.

Right, and one flattering data point from a group buy is not consistency. Consistency means separate batches, separately commissioned, over months.

kim_atl_prep said:

Six orders from the same supplier over eight months, every one independently tested, and the consistency is the part worth reporting rather than any…

This matches mine closely enough to be worth saying so. Prices dramatically below market are the strongest single signal, and the reason is arithmetic rather than suspicion. Synthesis, testing, and cold-chain shipping have floors. A price well under the floor means something was skipped, and the two things that get skipped are testing and content.

Adding the clinical framing, because it changes how the question reads.

Vendor reputation tracking for vendor vetting: I maintain a personal spreadsheet with every order I've placed — date, vendor, batch number, Janoshik result, personal efficacy assessment (1-5 scale), and any issues.

After 23 orders across 5 vendors: average purity 98.3%, zero sterility concerns, 0 shipping issues (all resolved). This data gives me confidence in my current source and documentation if issues arise.

I encourage everyone to track their orders systematically. Community data aggregation makes us all safer.